Method for the continuous casting of metal



United States Patent O METHOD FOR THE CONTINUOUS CASTING OF METAL IrvingRossi, Morristown, N. J., assignor to- Continuous Metalcast Co., Inc.,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationNovember 9, 1953, Serial No. 391,135

2 Claims. (Cl. 21-2001) This invention relates to the art of thecontinuous casting of metals.

'Continuous casting, as the name implies, connotes the continuousshaping or forming of liquid metal as it is cooled and solidified toform a casting of indefinite length. Ideally, the liquid metal should beshaped by a mold which is stationary with respect to the metal which itcontains, as in static mold casting. From the theoretical point of view,therefore, the ideal form of mold for continuous casting would be one ofunlimited length, but since this cannot exist in practice, other deviceshave been utilized.

Thus, it has been proposed to use endless supports such as revolvingdrums, wheels and the like, or endless moving bands or endless chains ofmold sections which join together to form a mold at the start of thesolidification process and separate at its conclusion to release thesolidifiedv metal. Since the surfaces of such movable supports canremain stationary with respect to the metal during along the axis of thecasting during the entire casting operation. This method of continuouscasting was foreshadowed by Pehrson as early as 1914, U. S. Patent No.1,088,171. Pehrson disclosed a mold which is activated by a cam oreccentric which imparts a simple harmonic motion thereto. As the moldadvances a rocker clamp grips the casting causing. it to advance withthe mold to the end of its advancing stroke. Then on the return strokeof the mold, the casting is released fromthe mold, but

is held stationary by another clamp until the mold begins its nextstroke.

The Pehrson process never achieved commercial success, and the followingfeatures may be noted as possibly or probably contributing to itsfailure. First, the advancing movement of the casting is intermittent.As disclosed by Pehrson, the casting advances only during one half ofthe total casting time. It remains stationary during the other half ofthe casting time. Second, the advancing movement of the casting is at avariable rate. Since the casting is advanced by a simple harmonicmotion, the rate of advance increases until the middle of the stroke andthen decreases until the end of the stroke. Third, the relative motionbetween the mold and casting which takes place on the return stroke ofthe mold is also at a variable rate, being at a maximum at the middle ofthe return stroke.

Other unfavorable factors may also have contributed to Pehrsons failure,but it may now be said that the above, at least would be consideredunfavorable in view of present knowledge.

A more successful method of utilizing a reciprocating mold is thatproposed by Junghans, U. S. Patent No. 2,135,183. Junghans proposed thatthe casting be withdrawn continuously at a constant rate, and that themold be advanced with the casting at the same rate as the casting sothat there is no relative motion therebetween during the advancingstroke of the mold. Then, at the end of the advancing stroke, the moldis quickly retracted, at an increased, but uniform rate, so that thereturn stroke requires much less time than the advancing stroke. Incommerical operation, the ratio of the time of the advancing stroke tothe time of the retracting stroke is usually of the order of three toone, so that the speed of the retracting stroke is three times the speedof withdrawal of the casting. I,

The Junghans process has been used commercially with great success,starting in Germany in 1936, in the United States in 1938 andsubsequently in many other countries of the world. It is unquestionablytrue that a vastly greater tonnage of metal has been cast successfullyby the Junghans process than by any other continuous casting process nowknown. The major portion of that tonnage has been in the non-ferrousfield, however, casting nonferrous metals and alloys such as brass,aluminum and aluminum alloys. Only recently has the use of the processbeen extended to the casting of steel, and here, as anticipated, newproblems have arisen.

One quite serious problem which has arisen is the problem of increasingthe casting rate to a level which is highly economical in the casting ofsteel. Another serious problem is one which arises as a directconsequence of increase in the casting rate, namely, the problem ofobtaining satisfactory surface characteristics.

One of the characteristics of castings produced by the J unghans processis the presence of rings extending around the casting in the surfacethereof. These rings are spaced at distances equal to the total advanceof the casting between successive strokes of the mold. That is, if thetotal advance of the casting (moving continuously at a constant rate) isten inches between the beginning of one advancing stroke of the mold andthe beginning of the next su cceeding advancing stroke, the rings willbe found to be spaced at ten inch intervals.

The rings are characterized by a roughened exterior surface, frequentlywith surface cracking, and frequently with evidence of bleeding, i. e.the leaking of molten metal through a lesion in formerly solidifiedmetal, with subsequent solidification of the leaking metal. The crystalstructure of the metal lying just under the rings is also irregular anddisturbed. The width of the rings, i. e. the distance lengthwise of thecasting through which these effects may be observed varies depending onthe conditions of the casting operation. With extreme care and operatingat a low casting rate, the effects may be minimized, but in geenral, thewidth of the rings is related to the time of the return stroke of themold. That is, if the return stroke consumes one fourth of the time ofthe complete cycle, the rings will be found to cover at least one fourthof the surface of the casting.

In the case of non-ferrous metals, these eflYects have been undesirable,but not too serious. in many cases, despite the surface imperfectionsthe castings could be rolled, extruded or otherwise processed withoutdifiiculty. In other cases a light scalping or other surfaceconditioning operation was sufiicient to remove all objectionablesurface imperfections. In the case of steel, however, such surfaceimperfections cannot be tolerated, and it is not economically feasibleto remove the imperfections by scalping. Moreover, the economicalcontinuous casting of steel demands a far greater casting rate than iscustomary or desirable in casting nonferrous metals, and it has beenfound that the increased casting rate greatly magnifies the difiiculty.Thus, in casting non-ferrous metals a casting rate of thirty to sixtyinches per minute is usually adequate, and at these speeds, the surfaceimperfections are tolerable in non-ferrous metals. In casting steel, onthe other hand, casting rates as high as two hundred inches per minutehave already been successfully achieved with the lunghans process, butthis success is tempered by the fact that at these speeds, the surfaceimperfections within the ring areas are extremely bad. Betweensuccessive rings, the surface is good and the interior crystallinestructure is excellent.

It is an object of the present invention to provide a method ofcontinuous casting, and particularly a method of mold reciprocation,which will mitigate the harmful effects of casting at high rates andreduce the sur face imperfections to a tolerable level.

Other objects and advantages of the invention will appear hereinafter.

In my early attempts to correct this difiiculty, the logical solutionappeared certainly to be to increase the speed of the return stroke ofthe mold in order to minimize the time period during which the mold ismoving in the opposite direction from the mold. Thereby, I reasoned, thewidth and probably also the unevenness of the rings would be reduced totolerable proportions.

Therefore, I proposed to change the time ratio of the advancing stroketo the return stroke from the usual three to one to four, five and evensix to one, the latter being almost the limit of mechanicalpracticability. Much to my surprise, however, the rings, and the surfaceimperfections evidenced thereby bccame progressively worse instead ofbetter. In some cases, instead of becoming narrower as might reasonablybe expected, the rings widened until they occupied almost 50% of thearea of the casting and the area within the rings was characterized byroughness, wrinkles, cracks, and bleed mg. l

According to the present invention, therefore, in order to solve theproblem, I have adopted the novel and seemingly illogical expedient ofreducing the speed of the re' turn stroke of the mold to a point suchthat the speed of the return stroke is never faster than the speed ofthe advancing stroke, and in many cases will be considerably slower thanthe speed of the advancing stroke. On the advancing stroke, the moldwill move with the casting at the same speed as the casting, and thecasting will move continuously at a constant rate. On the return strokeof the mold, the casting will continue to move continuously at aconstant rate, while the mold moves in the opposite direction at aconstant rate.

The contrast between the Junghans process and the method herein proposedmay be illustrated as follows. It may be assumed that steel is beingcast and that the casting rate (i. e. the rate at which the castingmoves continuously) is two hundred inches per minute. According to theJunghans process, and assuming the usual time ratio of advancing stroketo return stroke of three to one, since the mold will advance at therate of two hundred inches per minute, it must return at the rate of sixhundred inches per minute. And, since the casting continues to move atthe rate of two hundred inches per minute during the return stroke ofthe mold, the actual differential is six hundred plus two hundred, oreight hundred inches per minute.

If, in order to overcome the difiiculty, it is attempted to increase thespeed of the return stroke to give a time ratio of, say, six to one, thereturn stroke would be at the rate of twelve hundred inches per minute,and the actual differential of twelve hundred plus two hundred would befourteen hundred inches per minute.

According to the present invention, on the other hand, wherein the speedof the return stroke is never greater than the speed of the advancingstroke, and again assuming a casting rate of two hundred inches perminute, it will be seen that the maximum actual differential will be twohundred inches per minute (the maximum return speed of the mold) plustwo hundred inches per minute (the speed of the casting), or fourhundred inches per minute. This, it will be observed, is exactly onehalf of the actual differential which would exist on the return strokein the Junghans process.

If desired, however, the speed of the return stroke of the mold may bereduced even further. Thus, assuming again a casting speed of twohundred inches per minute, the return stroke of the mold may be at therate of one hundred inches per minute or even fifty inches per minute,in which cases the actual differentials would be three hundred inchesper minute or two hundred and fifty inches per minute, respectively.

In practice, the actual differential may be adjusted by the operatorafter inspection of the casting and taking into account the quality ofthe surface required during the casting of the particular metal which isbeing cast. In some cases greater perfection of surface is required thanin others, but the operator, applying the principles of this invention,and bearing in mind that the optimum condition for casting is the periodwhen the mold and casting are moving together, will be able to set thespeed of the return stroke to the maximum consistent with the surfacerequirements of the metal being cast, but always less than the castingspeed.

It will be understood that the invention may be var iously modified andembodied within the scope of the subjoined claims.

I claim as my invention:

1. A method for the continuous casting of metal which comprises pouringmolten metal continuously at a constant rate into one end of a castingmold, withdrawing solidified metal continuously at a constant rate of atleast two hundred inches per minute from the other end of said mold,advancing said mold with said solidified metal at the same rate at whichthe solidified metal is being withdrawn, so that there is no relativemotion between the solidified metal and the mold during the advancingstroke of the mold, and retracting said mold at a constant rate which isnever greater than the rate at which the mold is advanced.

2. A method for the continuous casting of metal as claimed in claim 1 inwhich the rate at which the mold is retracted is susbtantially less thanthe rate at which the mold is advanced.

References Cited in the file of this patent UNITED STATES PATENTS2,135,183 Junghans Nov. 1, 1938

1. A METHOD FOR THE CONTINUOUS CASTING OF METAL WHICH COMPRISES POURINGMOLTEN METAL CONTINUOUSLY AT A CONSTANT RATE INTO ONE END OF A CASTINGMOLD, WITHDRAWING SOLIDIFIED METAL CONTINUOUSLY AT A CONSTANT RATE OF ATLEAST TWO HUNDRED INCHES PER MINUTE FROM THE OTHER END OF SAID MOLD,ADVANCING SAID MOLD WITH SAID SOLIDIFIED METAL AT THE SAME RATE AT WHICHTHE SOLIDIFIED METAL IS BEING WITHDRAWN, SO THAT THERE IS NO RELATIVEMOTION BETWEEN THE SOLIDIFIED METAL AND THE MOLD DURING THE ADVANCINGSTROKE OF THE MOLD, AND RETRACTING SAID MOLD AT A CONSTANT RATE WHICH ISNEVER GREATER THAN THE RATE AT WHICH THE MOLD IS ADVANCED.